a. Field of the Invention
This invention relates to a temperature controller for a heater for a container for use in hazardous areas and to a method of programming such a temperature controller. In particular, this invention relates to a temperature controller for an induction heater or a flexible heating jacket for heating drums, containers, pipes or fittings in hazardous environments in which there is a significant risk of explosion.
b. Related Art
Large volume industrial containers, for example 40 imperial gallon (205 liter) drums or intermediate bulk containers (IBC's) which may have a volume of 1000 liters, are used to store a variety of different materials.
In some circumstances it is necessary or desirable to heat the containers and/or the contents of the containers, for example to decrease the viscosity of a liquid held within the container. It is known to provide a heating jacket or drum heater that surrounds the container and can be controlled to raise the temperature of the container and to maintain the temperature of the contents of the container at the desired temperature.
In some circumstances the contents of the containers may be hazardous or the environment in which the container is being heated is hazardous. In the United Kingdom a hazardous area is defined in The Dangerous Substances and Explosive Atmospheres Regulations 2002 as “a place in which an explosive atmosphere may occur in such quantities as to require special precautions to protect the health and safety of the workers concerned”. Equipment and in particular electrical and electronic equipment to be used in such hazardous areas is highly regulated and, in the United Kingdom, is covered by a number of European and British Standards. Within Europe these are covered by EU Directive 94/9/EC.
If containers and their contents are to be heated in a hazardous area there must, therefore, be strict control over the heating process and the equipment that is used. There may be a significant risk of explosion if the container is heated to too high a temperature or if a spark is created by the heating element or any of the components of the temperature controller.
A number of different types of heater for heating larger volume containers in hazardous areas are known.
Some heating jackets and drum heaters comprise an induction heater. These heaters have no heating element and have self limiting temperature control due to the induction process. These induction heaters are, however, only suitable for use with metal containers.
Heating jackets, for example flexible heating jackets, may be used to heat other types of container and these heaters include heating elements and a suitable thermostat, for example an adjustable capillary bulb thermostat. A typical thermostat, however, creates a spark that could ignite an explosive gas or dust and is, therefore, unsuitable for use in a hazardous environment. Options for temperature control in hazardous areas are generally expensive and complicated, and typically need to be located away from the heater in a safe area. In particular, explosion proof thermostats for fixed installations need to be fitted inside very heavy duty die-cast boxes which are not designed to be portable.
Furthermore, traditional thermostats can be slow to react to changes in temperature leading to the possibility of a significant overshoot of the desired operating temperature or set-point. The use of an electronic temperature controller may allow increased control of the temperature around the set-point; however, known controllers are too bulky and heavy to be fitted onto known heating jackets, especially flexible heating jackets.
Another disadvantage of known temperature controllers is that the settings, for example the set-point, are easily changed, which may result in an incorrect temperature being set and the container overheating.
It is, therefore, an object of the present invention to provide an improved temperature controller suitable for use with all types of heater and in hazardous environments.